Vibrato device for a musical instrument



Dec. 25, 1962 'r. B. GIBBS VIBRATO DEVICE FOR A MUSICAL INSTRUMENT Filedse t'. 26, 1958 3 Sheets-Sheet 1 Dec. 25, 1962 1'. B. GIBBS 3,069

VIBRATO DEVICE FOR A MUSICAL INSTRUMENT Filed Sept, 26, 195.8 3Sheets-Sheet 2 GENERATORS AMPLIFIER T. B. GIBBS VIBRATO DEVICE FOR AMUSICAL INSTRUMENT Filed Sept. 26, 1958 Dec. 25, 1952 3 Sheets-Sheet 3United States Patent Gfihce 3,hii9,957

Patented Dec. 25, 1952 VHERATQ DEVKQE EGR A MUSlCAL LNSTRUME NT ThomasE. Gibbs, false Delavan, Win, assignor to Gibbs Manufacturing 8;Research Eorporation, a corporation of Wisconsin Filed Sept. as, 1953,her. No. 763,643 3 Claims. (Cl. ti t-1.25)

This invention relates to an electronic musical instrument and moreparticularly to tremolo and vibrato systems for an electronic organ.

The terms tremolo and vibrato, while sometimes loosely consideredsynonymous, technically relate to two different, although related,musical effects. The tremolo, or tremulant, effect is one in which theamplitude of the musical tones is varied a slight amount above and belowthe mean value of the tone, at a low or subaudio rate. The vibratoeffect is one in which the frequency of the musical tones is variedslightly above and below the mean frequency, also at a low or subaudiorate. Where an instrument includes provision for both tremolo andvibrato, the two should operate in synchronisrn with both the amplitudeand frequency of the tones increasing and decreasing simultaneously.

it is a principal object of the present invention to provide anelectronic musical instrument with novel tremolo and vibrato systems,and a novel arrangement for synchronizing the operation of the twosystems.

One feature of the invention is the provision, in an electronic musicalinstrument, of means for generating and reproducing musical tones, meansfor varying the intensity of the tones to create tremolo effect, andmeans for varying the frequency of the tones to create a vibrato effect,the intensity and frequency varying means being synchronized, preferablyso that the intensity and frequency of the tones increase and decreasesimultaneously. Another feature is that the organ utilizes tonegenerators in which the light from a amp is scanned to produce themusical tones, and the intensity of the light and the speed of the scanare varied to produce the tremolo and the vibrato effects, respectively.

A further feature is the provision of an electronic musical instrumentin which the amplitude of the musical tones is effected by the intensityof a lamp, together with a tremolo control for varying the potentialapplied to the lamps, thereby varying the amplitude of the musicaltones. Still another feature is that the lamp is energized from a powersource having a resistor selectively connectable therewith for varyingthe amplitude of the potential applied to the lamp. Yet a furtherfeature is that the power source includes a filter having a capacitorselectively connecta-ble therein for varying the amplitude of thepotential applied to the lamp.

And another feature is the provision, in a musical instrument utilizinga tone generator having a moving element, the speed of which determinesthe frequency of the generated tone, of a vibrato system including meansfor varying the speed at which the moving element is driven, above andbelow the normal speed thereof. Yet a further feature is that the drivemotor for the moving element of the tone generator is resilientlymounted, and means are provided for oscillating the motor about itsdrive axis, as an actuating arm secured to the motor and en ageable withan eccentric cam driven by the motor. 7

Further features and advantages of the invention will readily beapparent from the following specification and from the drawings, inwhich:

FIGURE 1 is a diagrammatic sectional view illustrating the basicelements of a tone generator of the type with which the presentinvention may be used;

FIGURE 2 is an exploded fragmentary view of the mask and scanning discof FIGURE 1;

FIGURE 3 is a block diagram of the basic elements of a musicalinstrument with which the invention may be used;

FIGURE 4 is a schematic circuit diagram of an embodiment of the tremolosystem;

FIGURE 5 is an elevation view of the tone generator chassis of anelectronic musical instrument embodying the invention;

FIGURE 6 is an enlarged fragmentary view of the tone generator drive;

FIGURE 7 is an enlarged fragmentary view of the drive motor mounting,portions of the mechanism being eliminated in the interest of clarity ofillustration; and

FIGURE 8 is an enlarged fragmentary view of the tremolo and vibrato cam.

In FlGURES 1-3, certain basic elements of a preferred tone generator andmusical instrument are shown, as an illustration of the type finstrument with which the novel tremolo and vibrato systems of thepresent invention may be used. While certain features of the presentinvention are particularly adapted for use with the illustrated tonegenerator and instrument, the invention is also susceptible of use withother types of tone gen erators and musical instruments, as will readilybe apparent to those skilled in the art.

The basic elements of the preferred tone generator are illustrated inFEGURES l and 2. A mask 15 has formed thereon a series of lighttransmitting areas 16 which represent a particular tonal quality, theremainder of the mask being opaque. A scanning member 17, the majorportion of the surface of which is also opaque, is provided withscanning slots 1% which are moved past the tone representing area 16-,by rotation of the scanning member. A lamp l9 emits light which passesthrough lens 26, uniformly illuminatin the tone representing areas in ofthe As scanning member 17 moves past mask 35, the light from areas in isscanned by slots if} and the resulting light variations impinge on aphotosensitive device or photocell 21, which in turn converts the lightvariations to electrical signal variations appearat terminals 22. Thetone generator is provided with a plurality of light transmitting maskareas, each with its own light source, for producing notes of differingtonal qualities, and by proper arrangement of tone representing areasand scanning slots, covering several frequencies.

in FIGURE 3, the basic elements of an electronic organ are shown. Aplurality of tone generators 23 are connected through stop selectors 2with keys 25. A preferred organ arrangement has twelve tone generators,one for each note in an octave. When a key 25 is pressed, certain lampsin the proper tone generator are energized, depending on the stops whichhave been selected. The resulting light variations are converted toelectrical signals by the photocell in the tone generator, theelectrical signals amplified and broadcast in audible form by speaker 12The power source for the tone generator lamps 19, of which there may beseveral hundred, is illustrated in FiGURE 4. The power source isenergized from a suitable source of power, as volts A.C., connectedthrough leads 3d and 31 to the primary winding 32a of a low voltagepower transformer 32. Secondary winding 32b of the transformer is centertapped and connected with a full wave rectifier circuit includingselenium rectifiers 33 and 34. A filter circuit includes series inductor35 and shunt capacitor as connected with the center tap and returned toa reference potential or ground 37. The tone generator lamps 19 areconnected in parallel (through the key switch-stop selector mechanism,not shown in FIGURE 4) and across capacitor 36.

Even very slight variations in the potential applied to the toneenerator lamps cause a change in the intensity of the light thus in theamplitude of the generated signal. Accordingly, the filter of the powersupply is such that the alternating component of the voltage in theoutput of the rectifiers is substantially completely eliminated. Thesimple single stage of inductance-capacitance filtering shown herein isintended merely to represent an adequate filter, and the actual filterused may include several similar sections.

The sensitivity of the tone generators to variations in the potentialapplied to lamps 19 is utilized in the system illustrated by the circuitof FIGURE 4 to provide a tremolo effect. In order to achieve a tremolohaving both an increase and a decrease of the amplitude of the generatedtones, above and below the nominal or normal value thereof when thetremolo system is not in operation, it is necessary that the outputvoltage of the power supply be increased above and decreased below itsnormal value. As will appear in detail below, this is accomplished bymaking two changes in the power supply circuit. First, a capacitor isshunted across the input of the filter to raise the output potential;and second, a resistor is connected in series with an input lead to thepower supply to decrease the output potential. These two elements arealternately switched into the circuit, causing the potential applied tolamps 19 to vary above and below its value when the tremolo circuit isinoperative.

The capacitor, indicated at 38, is connected in series with a currentlimiting resistor 3E and through switch 49 to ground. Switch is operatedat a low or subaudio rate, as four cycles per second by a cam 41 whichpreferably forms a part of the tone generator drive system, as willappear. Resistor 42 is coupled through transformer 43 with input lead 3%of the power supply. A shunt circuit shorting resistor 42 isintermittently completed by switch 44, which is mechanically ganged withswitch 40 so that they operate in synchronism. When switches 4i} and 44are closed, capacitor 33 is connected in the circuit increasing theoutput voltage of the power supply, and resistor 42 is shunted. Whenboth switches are open, capacitor 38 is removed from the circuit andresistor 42 is effectively connected in the power supply input circuitreducing the output potential. By properly correlating the size ofcapacitor 38 and resistor 42, the increase and decrease in the amplitudeof the musical tones may be made substantially equal so that a uniformvariation above and below the normal amplitude is produced.

The operation of the tremolo circuit is controlled by a switch 45 shownin the tremolo On position. In this position, it completes the circuitfor capacitor 355, to ground 37. In the Off position of the switch, themovable arm 45 completes a shunt circuit shorting resistor 42.

In a specific embodiment of the tremolo circuit, capacitor 38 has avalue of 2000 microfarads and current limiting resistor 3? a value of0.120 ohm. Resistor 4-6, 18 ohms, is connected across the contacts ofswitch 40, so that the switch will not have to carry all of the currentthrough capacitor 38. However, this resistance is so high as comparedwith the reactance of the capacitor 38 and the other shunt elements inthe power supply, that it has no appreciable effect on the operation ofthe circuit when switch 49 is opened. A capacitor 47, 4 f. (microfarad)shunts switch 4t Resistor 42 has a value of 166 ohms, and transformer aone-to-one turn ratio.

FIGURE 5 illustrates a drive arrangement for a preferred form of musicalinstrument incorporating the tone generators of FIGURES l and 2. Twelvetone generators 50, one for each note of the octave, are mounted on atone generator panel 51 with drive pulleys a, for the rotatable maskmembers 17, extending rearwardly therefrom. The pulleys 559a areconnected by an endless drive element 52 which also passes aroundadjustable idler wheel 53 to permit the necessary tension to beestablished. A drive motor 54 is mounted below the generator panel 51and connected by drive belt 55 with a pulley 56 mounted on the shaft ofone of the tone generators.

in FiGURE 7, it will be seen that the mount for motor 54 includes abracket 58 secured to a support member 59. A clarnp which has twoportions 6% and 61 and an adjusting screw 62 is carried from the lowerend of bracket 58, supporting a metal ring 63 within which is a motormounting element 64- of resilient material, as rubber. The motormounting element has a plurality of inwardly extending deformablefingers 64a which engage surfaces 65 formed on the end bell 66 of drivemotor 5- This arrangement shown for one end of the motor is repeated atthe other end.

The drive shaft of the motor 54 carires a pulley 68 which is connectedthrough drive belt with pulley 56 on the shaft 69 of one of the tonegenerator drive pulleys 51m. The other tone generators are driven frommotor 54 through belts 55 and 52. The resilient mounting of rnotor 54permits it to be rocked about its drive axis to vary the speed of drivebelts 55 and 52. Secured to a pair of studs 70 and 71 which extendoutwardly from the shell of motor 54 is an arm 72 having an actuatingportion or cam follower 73. The arm portion 73 carries a bearing surface74 engageable with an eccentric cam carried by shaft 69. Drive surface7:-

held in contact with the cam by spring 76 connected between the upperend of arm portion 73 and fixed member 77. As cam turns, arm portion 73moves back. and forth parting an oscillatory motion of several degreesextent to rnotor 54. This oscillatory motion is transmitted to the drivebelt 55, modifying or modulating the constant speed of drive belt 52 andof the rotating scanning discs of each of the tone generators. The speedof drive belt 55 is increased above and decreased below its normalspeed, transmitting a similar increase and decrease to the scanningdiscs of the tone generators. This results in a frequency modulation ofthe generated tone representing signals at a low or subaudio rate. Cam75 has slotted mounting openings 75a therein, permitting adjustment ofthe amplitude of the frequency shift in the generated tones, above andbelow the normal frequency of the tones.

In order to render the vibrato inoperative, the bearing surface 74 ofarm portion 73 is moved out of contact with cam 75 by energizing anelectromagnet 78 which attracts an armature 79 carried at the end of armportion 72. Movement of armature 79 upwardly moves bearing surface 74 tothe left, against the action of spring 76. Deenergization ofelectromagnet 78 releases the arm, allowing spring 76 to move bearingsurface 74 to the right into engagement with cam 75.

As pointed out above, where an organ is provided with both tremolo andvibrato systems, it is desirable that the operation of the two systemsbe synchronized, so that both the amplitude or intensity of thegenerated tones and the frequency thereof increase and decreasesimultaneously. Accordingly, switches 40 and 44 in the tremolo circuit(FIGURE 4) are arranged for actuation by cam 75, as shown in FIGURE 8.Cam follower St} bears against the surface of cam 75 and actuates theswitch operating member 81.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable of many modifications. Changestherefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as disclosed in theappended claims.

I claim:

1. In an electrical musical instrument, a plurality of tone signalgenerators of the type which have rotatable members the speed ofrotation of which determines the pitch of the tones generated, anelectric motor having a frame and a shaft which rotates at a constantspeed with respect to the frame, drive transmission means connectingsaid motor shaft to said rotatable members for driving each of saidrotatable members individually at a speed which is a constant functionof the speed of said motor shaft, means mounting said motor frame forrocking movement about the axis of said shaft, oscillatory meansconnected to be driven by said motor shaft and adapted when activated torock said motor frame in substantially a simple harmonic manner aboutthe shaft axis at a vibrato frequency, and means operable at will fordeactivating said oscillatory means and for holding said motor frame insubstantially a fixed position. i

2. In an electrical musical instrument, a plurality of tone signalgenerators of the type which have rotatable members the speed ofrotation of Which determines the pitch of the tones generated, anelectric motor having a frame and a shaft which rotates at a constantspeed with respect to the frame, drive transmission means connectingsaid motor shaft to said rotatable members for driving each of saidrotatable members individually at a speed which is a constant functionof the speed of said motor shaft, means mounting said motor frame forrocking movement about the axis of said shaft, oscillatory cam meansconnected to be rotated by said motor shaft, a cam follower secured tosaid motor frame and adapted to bear against said cam to rock said motorframe about the shaft axis at a vibrato frequency in response torotation of said cam, and means operable at will for swinging said camfollower away from said cam and for holding said motor frame insubstantially a fixed position.

3. In an electrical musical instrument, a plurality of tone signalgenerators of the type which have rotatable members the speed ofrotation of which determines the pitch of the tones generated, anelectric motor having a frame and a shaft which rotates at a constantspeed with respect to the frame, drive transmission means connectingsaid motor shaft to said rotatable members for driving each of saidrotatable members individually at a speed which is a constant functionof the speed of said motor shaft, means mounting said motor frame forrocking movement about the axis of said shaft, oscillatory cam meansconnected to be rotated by said motor shaft, a cam follower secured tosaid motor frame and adapted to bear against said cam to rock said motorframe about the shaft axis at a vibrato frequency in response torotation of said cam, electromagnetic and armature means adapted forswinging said cam follower away from said cam and for holding said motorframe in substantially a fixed position in response to energization ofsaid electromagnetic means, and circuit means operable at will forenergizing or deenergizing said electromagnetic means.

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